In, for example, coal mines it is usual for the mining operation to form a network of spaced apart passages such as shown schematically in FIG. 1.
Typically a first passageway 1 is utilized to provide ventilation to the active mining face and a second passageway 2 is utilized to provide a ventilation return path from the face.
Cross passages 3 communicating between the first and second passageway are closed in order to improve the ventilation flows, but the closure 4 must include a door or trapdoor 5 openable to permit a man to pass therethrough in the event of an emergency.
Mine passages are not of uniform dimension, nor of uniform cross-section, and in fact are liable to change in cross-section as time passes due to floor heave or roof pressure. Therefore each doorway frame is presently individually constructed at the desired location from timber. Each of two timber pillars is first cut to approximate size, next wedged upright in place between the roof and the floor, and then doorway frame members are constructed and mounted to the pillars and a suitable door supported therefrom. The space between the doorway frame and the surrounding passage wall is then bricked up, or otherwise sealed. Typically each such construction involves 2 men for a day.
In addition it is sometimes desired to provide partial closure of a passageway to balance the ventilation system.
In that event it has been usual to partially close the passage with brick walls leaving an opening which in turn is partially closed by a cladding material for example by fibro cement or timber loosely nailed to battons. The sheets are arranged to leave an unclad opening having an area determined by aerodynamic measurement to provide balanced ventilation.
Each shift, inspectors are required to pass through the passage. To do so they must remove the cladding sheets and do not always return them to the correct position. The ventilation openings are the subject of regulations and if adjustable must be locked by mine management.